Coastal Radio Happenings

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    Shirley Knott

    Because of 4 other co or adjacent channel stations within 500 km, KDUN is hemmed in to the north. With a station already at 1050 in Eugene, they’d have to be careful with where the transmitter is built.

    I don’t do AM applications, but it seems that something with at least 2 towers could send a good signal West Southwest from somewhere NW of Eugene. This would need to protect stations in Tigard, Milwaukie, Shelton WA and Eugene.

    Also, a decent night power would likely be possible to protect stations in Iowa and too many other to mention, and of course, WBZ Boston. Spilling the main lobe out over the ocean is a time honored tradition for shoe horning 50 kW into a space previously occupied by 5 kW.

    The quote from Delilah that I saw in Radio World mentioned ‘update and upgrade.’ I’m fairly sure this is code for getting back on the air ASAP, then moving to someplace with an economy.

    • This reply was modified 2 months, 2 weeks ago by Shirley Knott.

    The subject came up on another thread on spacing and duplexing AM’s. Correct me if I am wrong, with FM’s full-power spacing is 4 channels. You can put a translator up as long as there are 2 channels of spacing on either side. (Do I have this part right?) We have stations on 89.1, 89.5, 89.9, etc. In Portland, there is a 1040 AM and in Eugene there is a 1050 AM. How close can 1030 be to either of those stations?


    I’m not an engineer, just an old jock/programmer. What does this mean:

    Frequency separation (kHz) Contour of proposed station (classes B, C and D) (mV/m) Contour of any other station (mV/m)
    0 0.005
    0.500 0.100 (Class A).
    0.500(Other classes).
    0.025 (All classes).
    10 0.250
    0.500 0.500(All classes).
    0.250 (All classes).
    20 5
    5 5 (All classes).
    5 (All classes).
    30 25 25 (All classes).

    Shirley Knott

    AM doesn’t have mileage separations. It’s all based on signal strength to reduce mutual interference.

    A proposed station’s predicted signal can’t be larger than an existing station’s signal at the predicted points given in the chart. Lower mutual signal levels are on first adjacent channels 10 kHz removed. Even lower mutual signal levels on second adjacents 20 kHz removed from the proposed station.

    The charts are a useful tool if you have predicted coverage maps for the affected stations. Otherwise, it’s just conjeture and SWAG work.

    What this tells me is that KDUN 1030 can’t put more than a 5 mV/m signal over the KORG 1050 Eugene signal around Eugene. So my initial guess at their plan for KDUN cover Eugene was incorrect. It could still have a listenable signal, but not competitive beyond the DX market.

    Based on the cost of electricity, my new SWAG is that KDUN will go with a second or third tower array with a strong signal into Coos Bay that doesn’t waste electricity aimed east over the Coast Range or west over the Pacific.

    Maybe even 5 kW would work for them. They still have to protect existing stations, but something with laser focus along the coast could probably do the trick and cover an equivalent population with a more manageable power bill.

    I’d compare it to the highly directional AM Mexican based border blasters with almost no signal into Mexico, and perhaps an Effective Radiated Power of a million Watts coming into the U.S. The tight beam is pointed at San Diego and Los Angeles.

    What you spend on towers and phasing equipment, you save in a short time on electricity if your engineering consultant is smart and your proposed channel isn’t already plugged by the neighbors. Not everybody needs 50 thousand Watts in a smaller market.

    • This reply was modified 2 months, 2 weeks ago by Shirley Knott.
    Shirley Knott

    One FCC practice that confuses newbies is that in FM work, the FCC considers the highest power in any direction as the Effective Radiated Power, or ERP.

    In AM work, the FCC uses the licensed transmitter output power as the station power. A station with a directional pattern will have an ERP much higher than the station power in at least one direction, with a corresponding lower power in a different direction. This is generally done to squeeze a station into a hole that permits a higher signal level over the community of license, and lower power toward a previously licensed station.

    But some of the earliest directional stations were on the east coast. They had transmitter sites between the ocean and the big city. They were the original Class A channels and didn’t have to protect anybody. But rather than waste power over the ocean, they used directionality to increase signal strength over the land mass. I believe WBZ 1030 in Boston and WABC 770 in New York were early adopters.

    I knew a guy who was an engineer at WBZ back in the 60s’ They had a temporary problem with their directional antenna and had to operate from a single tower for awhile. They were amazed to start getting QSL reception reports from Great Britain during the repairs.

    • This reply was modified 2 months, 2 weeks ago by Shirley Knott.

    Thanks, Shirley!

    Andy Brown

    “and WABC 770 in New York”

    Nope. Not them. 770 has a single half wave (653 feet) tower that was built in 1943. They have never been directional.

    “In AM work, the FCC uses the licensed transmitter output power as the station power.”

    That is incorrect. The licensed (aka “nominal”) power for an AM station is not transmitter power. It is equal to antenna power (power being delivered to the antenna (tower) for N.D. or common point for D.A.) which is equal to transmitter power output (TPO) minus losses in the transmission system (cable and tuning network). AM licensees are allowed to make up for these losses by raising TPO above the licensed power. How much depends on station class. TPO is always going to be greater than licensed power.

    Antenna power is measured at the base of the tower for non directional and at the common point for directional antennae systems.



    So a 50 kW flamethrower with a perfectly tuned directional array (50 Ω + j0) is allowed 105.3% of licensed power. The power at the common point would be 52.650 kW (measured with a common point ammeter that would be the square root of 52,650/50 or 32.45 amps). In non directional systems (one tower), the tower impedance can be all over the board although historically as close to 100 Ω used to be the target. So the actual TPO is whatever it takes to push the required amps as measured at the antenna base (after the tuning gear in the doghouse, i.e. the tower base meter is the last thing before the actual antenna/tower connection).

    The common point is where the phasor cabinet is, i.e. the place where the transmitter output is split to be fed to the various towers in the antenna array.

    This is all separate and apart from the operating window of 5% above and 10% below the parameters determined above.

    This might be helpful:

    So in AM the transmitter power will always be more than the licensed power. 5 kW stations are allowed 8% to cover losses.

    FM/TV is similar. Transmission line losses are always taken into account and there are various ways of measuring power, also in FM/TV there is antenna gain to be accounted for.


    And thank you, Andy!

    Shirley Knott


    • This reply was modified 2 months, 2 weeks ago by Shirley Knott.
    • This reply was modified 2 months, 2 weeks ago by Shirley Knott. Reason: no point flaming a flamer
    Andy Brown

    The post below was written in response to Shirley Knott’s post above attempting to insult me for correcting some of his obvious errors in terminology and procedure, the text to which he has removed so as to not let you all know what kind of guy is hiding behind that dumb handle.

    You’re dumbing it all down and that is what creates the confusion. That’s not educating anyone, who ever you are.

    You’re wasting your bits insulting me. Clearly I know more about this stuff than you ever will and know how to explain it to anyone. You haven’t been on this board all that long. You’re excused.

    • This reply was modified 2 months, 2 weeks ago by Andy Brown.
    Shirley Knott

    Andy, I didn’t want to start a flame war with a bully such as yourself. Yes, you are an engineering god. I met a few when I was engineering in Los Angeles. But only one of them had serious personality problems like yours.

    My explanation did not ‘dumb it down.’ It made it simpler for non-engineers to maybe grasp the concept. Your convoluted meanderings into how various operations figure out their radiated power had ABSOLUTELY NOTHING to do with the question at hand, which was what do these AM overlap charts mean? This is a point that you and your ego apparently missed.

    You’re a loose cannon with a serious need for recognition. But I think everybody on this board already knows that.

    I was angry with your holier than thou attitude aimed at me this time. You’re a bully with a bad attitude. I know it’s a waste of time insulting you which is why I removed the post. You are full of knowledge or something, but the imperious nature of most of your posts is hard for me to deal with.

    You’ve apparently set yourself up as the king of this board, at least in your own mind. Have at it.

    You impress me a lot. But not favorably.

    Andy Brown

    Your explanation was indeed a crude attempt at dumbing it down and most of the folks here know it. Terminology matters when you are trying to explain complicated technical matters. Get it right or be corrected. That’s what really got you mad. Someone corrected you. Call the wambulance. Insulting me will get you nowhere. Take your bombast and go back to L.A. where you can continue to shed bad explanations unfettered by those that really know what they’re talking about. Go ahead, take your last shot. I’m KDUN here.


    Shirley, you jest! 🙂


    Apprearing at MCH Enterprises media brokerage website today is the following listing:

    “NEW! OREGON COAST NON-COMMERCIAL FM WITH NON-COMMERCIAL BAND TRANSLATOR. Both stations are licensed to the non-commercial band, on the coast. The Translator is “unbound” and can be purchased separately. The asking price for the FM and the FX is only $100,000. The primary FM is a Class A facility and the FX operates with 130 watts. No office/studio and comes with the receive end of a Barix system.”

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